Class is not abstract and does not override abstract method in superclass

Question

I am working on a generic implementation of the Genetic Algorithm. I'm trying to extend a specific Individual for the knapsack problem from the abstract class Individual

package GenericGA;

public abstract class Individual {

    private double fitness;
    private double probability;


    public double getFitness() {
        return fitness;
    }

    public double getProbability() {
        return probability;
    }

    public void updateProb(double totalFitness){
        probability = fitness/totalFitness;
    }


    abstract void updateFitness();
    abstract Individual crossover(Individual partner);
    abstract void mutate(double mutationRate);

}

This is the extended class

package GenericGA.SpecificImplementations;


import GenericGA.Individual;

public class KnapsackIndividual extends Individual {


    void updateFitness(){

    }

    Individual crossover(Individual partner){
        return null;
    }

    void mutate(double mutationRate){

    }

    public static void main(String[] args){
        System.out.println("Hello");
    }

}

Since I was using intellij and it was giving me the error, I thought that could be a problem of the IDE, so I compiled with javac and I get the same error:

GenericGA.SpecificImplementations.KnapsackIndividual is not abstract and does not override abstract method mutate(double) in GenericGA.Individual

There are no spelling mistakes and the signatures are correct, and I get the error also for the other abstract methods when removing the mutate method that is giving the error.

Moreover if I use @Override on top of the methods, it says

Method does not override method from its superclass

What am I missing here?

Thanks in advance.

Answer 1

It looks like your abstract mutate method is not visible to the sub-class, since it has default access (which is package private), and the KnapsackIndividual sub-class is in a different package.

Change the abstract method to:

protected abstract void mutate(double mutationRate);

and change the overriding method accordingly:

@Override
protected void mutate(double mutationRate){

}